Various chemical and physical processes, e.g. polymerization processes, petroleum cracking processes, heat exchange processes, etc., can be automatized by controlling one or more parameters of these processes. Generally speaking, in a control method a disturbance variable is sensed and responsive thereto a manipulated variable is regulated such as to reach a desired behavior of a process parameter. In most instances, it is desirable to keep a certain process parameter, e.g. a temperature or a conversion rate, constant.
The control systems and methods can essentially be divided into two groups. The first group, the feedback controls, are methods in which a control signal is generated after the parameter of the process which is to be controlled shows a deviation from the function or value this parameter is supposed to have. The second group, the feedforward controls, are methods in which variables of a process are sensed before they become effective on the parameter to be controlled and a control operation is taken to prevent a deviation of the parameter from the value. Modern control systems and methods combine both the feedback and the feedforward control to obtain more accurate results.
Every control method starts from a given process and a model or functional relationship by which responsive to every disturbance variable change a certain control operation is carried out. Thus, the process and the control method are connected. However, the functional relationship has to be determined separately for every process. In addition, once this functional relationship is established, it is generally impossible to further improve the control method without either establishing a completely new functional relationship or operating with additional control methods. It would thus be highly desirable to have a control method available that can be applied to a wide variety of processes and in which only the constants of the functional relationship mentioned differ, in which these constants, however, are defined by a few constants of the process dynamics.